On the evolution of the molecular gas fraction of star-forming galaxies

J.E. Geach, I. Smail, S.M. Moran, L.A. Macarthur, Claudia Lagos Urbina, A.C. Edge

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    We present IRAM Plateau de Bure interferometric detections of CO(J = 1 → 0) emission from a 24 μm-selected sample of star-forming galaxies at z = 0.4. The galaxies have polycyclic aromatic hydrocarbon 7.7 μm-derived star formation rates of SFR ∼30-60 M⊙ yr-1 and stellar masses M* 1011 M. The CO(J = 1 → 0) luminosities of the galaxies imply that the disks still contain a large reservoir of molecular gas, contributing ∼20% of the baryonic mass, but have star formation "efficiencies" similar to local quiescent disks and gas-dominated disks at z ∼ 1.5-2. We reveal evidence that the average molecular gas fraction has undergone strong evolution since z ∼ 2, with f gas (1 + z)∼2±0.5. The evolution of f gas encodes fundamental information about the relative depletion/replenishment of molecular fuel in galaxies and is expected to be a strong function of halo mass. We show that the latest predictions for the evolution of the molecular gas fraction in semi-analytic models of galaxy formation within a ΛCDM universe are supported by these new observations. © 2011. The American Astronomical Society. All rights reserved.
    Original languageEnglish
    Pages (from-to)19
    JournalAstrophysical Journal Letters
    Issue number2 PART II
    Publication statusPublished - 2011


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